The present invention relates to a semiconductor memory and a method for fabricating the same, and more particularly, it relates to a memory cell structure of a semiconductor memory using a high-κ film or a ferroelectric film.
Recently, for multimedia equipment required to have a large memory capacity and a high data transfer rate, embedded-DRAM processes for combining DRAMs with a high performance logic circuit has been practically employed.
In conventional DRAM process, however, since it is necessary to perform high temperature annealing for forming a capacitor insulating film of a capacitor working as a memory capacitor, the impurity concentration profile of impurity diffusion layers of a transistor included in a high performance logic circuit can be disadvantageously degraded through this high temperature annealing. Also, in process for merely a memory such as a DRAM or a FeRAM, high temperature annealing is preferably avoided for reducing the size of a memory cell transistor.
Therefore, it is indispensable to develop a MIM (Metal-Insulator-Metal) capacitor using, as a capacitor insulating film of a memory capacitor, a high-κ film that can be formed at a low temperature and can provide a fine memory cell. An example of the high-κ film is a dielectric film having a perovskite structure such as a BST ((BaSr)TiO3) film. On the other hand, as a material for a metal electrode of the MIM capacitor, Pt with high oxidation resistance is generally regarded as a promising material. Also, dielectric films with the perovskite structure, such as a SBT (SrBi2Ta2O9) film and a BTO (Bi4Ti3O12) film, are well known as ferroelectric films.
The conventional MIM capacitor serving as a memory capacitor has, however, the following problems:
When a contact hole is formed to reach a Pt electrode (upper electrode) provided on a capacitor insulating high-κ film film, a reducing atmosphere and the like employed in forming a contact plug may harmfully affect the characteristic of the capacitor. In general, most of dielectric films are oxides, and hence, oxygen included in such a dielectric film may be lost due to the reducing atmosphere. In particular, when the capacitor insulating film is a high-κ film or a ferroelectric film, there is high possibility of the oxygen loss. Particularly in a dielectric film with the perovskite structure, the characteristic can be largely degraded due to the oxygen loss.
Furthermore, in fabrication of devices such as a DRAM that conventionally do not use a Pt electrode, it is difficult to use the existing facilities for, for example, forming a contact reaching a Pt electrode that is newly used, and hence, such a procedure need to be performed by using dedicated facilities. This is for the following reason: For example, in forming a contact hole connected to a Pt electrode through an interlayer insulating film, Pt is sputtered when the Pt electrode is exposed, and hence, Pt is adhered onto the walls and members within a chamber. If this chamber is used for another process without any treatment, the Pt enters an active region or the like of a transistor, which can harmfully affect the operation of the transistor.